Electrode for secondary battery, secondary battery and cable-type secondary battery comprising the same

ABSTRACT

The present invention provides an electrode for a secondary battery, more specifically an electrode for a secondary battery, comprising a current collector; an electrode active material layer formed on at least one surface or the whole outer surface of the current collector; a conductive material-coating layer formed on the top surface of the electrode active material layer and comprising a conductive material and a first polymer binder; and a porous coating layer formed on the top surface of the conductive material-coating layer and comprising a second polymer binder. Also, the present invention provides a secondary battery and a cable-type secondary battery comprising the electrode

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/KR2013/011511 filed on Dec. 12, 2013, which claims priority under 35USC 119(a) to Korean Patent Application No. 10-2012-0144394 filed in theRepublic of Korea on Dec. 12, 2012, and Korean Patent Application No.10-2013-0154427 filed in the Republic of Korea on Dec. 12, 2013, thedisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electrode for a secondary battery,more specifically to an electrode for a secondary battery which canprevent the release of an electrode active material layer and increasethe conductivity of an electrode to enhance the cycle lifecharacteristics of the battery, a secondary battery and a cable-typesecondary battery comprising the electrode.

BACKGROUND ART

Secondary batteries are devices capable of storing energy in chemicalform and of converting into electrical energy to generate electricitywhen needed. The secondary batteries are also referred to asrechargeable batteries because they can be recharged repeatedly. Commonsecondary batteries include lead accumulators, NiCd batteries, NiMHaccumulators, Li-ion batteries, Li-ion polymer batteries, and the like.When compared with disposable primary batteries, not only are thesecondary batteries more economically efficient, they are also moreenvironmentally friendly.

Secondary batteries are currently used in applications requiring lowelectric power, for example, equipment to start vehicles, mobiledevices, tools, uninterruptible power supplies, and the like. Recently,as the development of wireless communication technologies has beenleading to the popularization of mobile devices and even to themobilization of many kinds of conventional devices, the demand forsecondary batteries has been dramatically increasing. Secondarybatteries are also used in environmentally friendly next-generationvehicles such as hybrid vehicles and electric vehicles to reduce thecosts and weight and to increase the service life of the vehicles.

Generally, secondary batteries have a cylindrical, prismatic, or pouchshape. This is associated with a fabrication process of the secondarybatteries in which an electrode assembly composed of an anode, acathode, and a separator is mounted in a cylindrical or prismatic metalcasing or a pouch-shaped casing of an aluminum laminate sheet, and inwhich the casing is filled with electrolyte. Because a predeterminedmounting space for the electrode assembly is necessary in this process,the cylindrical, prismatic or pouch shape of the secondary batteries isa limitation in developing various shapes of mobile devices.Accordingly, there is a need for secondary batteries of a new structurethat are easily adaptable in shape.

To fulfill this need, suggestions have been made to develop cable-typebatteries having a very high ratio of length to cross-sectionaldiameter. The cable-type batteries are easy in shape variation, whilebeing subject to stress due to external force for the shape variation.Also, the electrode active material layer of cable-type batteries may bereleased by rapid volume expansion during charging and dischargingprocesses. From these reasons, the capacity of the batteries may bereduced and the cycle life characteristics thereof may be deteriorated.

In order to overcome such a problem, the electrode active material layermay further have a coating layer of a polymer binder on the top surfacethereof. The coating layer of a polymer binder can improve the cyclelife characteristics of batteries, but may increase electrode resistancedue to the substantial absence of pores present in the coating layer toinhibit the introduction of an electrolyte solution in an electrodeactive material layer.

Disclosure Technical Problem

The present invention is designed to solve the above-mentioned problems,and therefore it is directed to providing an electrode for a secondarybattery, which can prevent the release of an electrode active materiallayer and increase the conductivity of an electrode to enhance the cyclelife characteristics of the battery, and also can allow the goodintroduction of an electrolyte solution in an electrode active materiallayer to prevent the increase of electrode resistance; and a secondarybattery and a cable-type secondary battery comprising the electrode.

Technical Solution

In accordance with one aspect of the present invention, there isprovided an electrode for a secondary battery, comprising a currentcollector; an electrode active material layer formed on at least onesurface or the whole outer surface of the current collector; aconductive material-coating layer formed on the top surface of theelectrode active material layer and comprising a conductive material anda first polymer binder; and a porous coating layer formed on the topsurface of the conductive material-coating layer and comprising a secondpolymer binder.

The current collector used in the electrode of the present invention maybe a planar form, a hollow form, a wire form, a wound wire form, a woundsheet form or a mesh form.

The conductive material and the first polymer binder in the conductivematerial-coating layer may be present in a weight ratio of 1:10 to 8:10.

The conductive material-coating layer may have pores having a size of0.01 to 5 μm, and may have a porosity of 5 to 70%.

The conductive material may comprise any one selected from the groupconsisting of carbon black, acetylene black, ketjen black, carbon fiber,carbon nanotube, graphene and a mixture thereof.

Also, the first polymer binder may be selected from the group consistingof polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP),polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidenefluoride-co-trichloroethylene, polybutyl acrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate,polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate,cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.

Meanwhile, the porous coating layer may have pores having a size of 0.01to 10 μm, and may have a porosity of 5 to 95%.

The porous coating layer may further comprise inorganic particles.

In this case, the inorganic particles and the second polymer binder inthe porous coating layer may be present in a weight ratio of 10:90 to95:5.

The inorganic particles may be inorganic particles having a dielectricconstant of 5 or higher, inorganic particles having the ability totransport lithium ions, or a mixture thereof.

Examples of the inorganic particles having a dielectric constant of 5 orhigher include BaTiO₃, Pb(Zr_(x), Ti_(1-x))O₃(PZT, 0<x<1),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),(1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (PMN—PT, 0<x<1), hafnia (HfO₂),SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, SiO₂,AlOOH, Al(OH)₃, TiO₂ and a mixture thereof.

Also, examples of the inorganic particles having the ability totransport lithium ions include lithium phosphate (Li₃PO₄), lithiumtitanium phosphate (Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3), lithium aluminumtitanium phosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃, 0<x<2, 0<y<1, 0<z<3),(LiAlTiP)_(x)O_(y) type glass (0<x<4, 0<y<13), lithium lanthanumtitanate (Li_(x)La_(y)TiO₃,0<x<2, 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5),lithium nitride (Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass(Li_(x)Si_(y)S_(z), 0<x<3, 0<y<2, 0<z<4), P₂S₅ type glass(Li_(x)P_(y)S_(z), 0<x<3, 0<y<3, 0<z<7) inorganic particles, and amixture thereof.

The inorganic particles may have an average diameter of 10 nm to 5 μm.

Also, the second polymer binder may be selected from the groupconsisting of polyvinylidene fluoride (PVDF), hexafluoro propylene(HFP), polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidenefluoride-co-trichloroethylene, polybutyl acrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate,polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate,cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.

Meanwhile, the electrode for a secondary battery may be an anode.

In this case, the electrode active material layer may comprise an activematerial selected from the group consisting of metals (Me) including Si,Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce, Cu, Co, Ni andFe; alloys of the metals; oxides (MeOx) of the metals; and a mixturethereof.

In accordance with another aspect of the present invention, there isprovided a secondary battery comprising a cathode, an anode, a separatorinterposed between the cathode and the anode, and a non-aqueouselectrolyte solution, wherein the anode is the electrode for a secondarybattery according to the present invention.

In accordance with still another aspect of the present invention, thereis provided a cable-type secondary battery having a horizontal crosssection and extending longitudinally, and comprising: a core forsupplying lithium ions, which comprises an electrolyte; an innerelectrode comprising an open-structured inner current collectorsurrounding the outer surface of the core for supplying lithium ions, aninner electrode active material layer surrounding the outer surface ofthe inner current collector, a conductive material-coating layer formedon the outer surface of the inner electrode active material layer andcomprising a conductive material and a first polymer binder, and aporous coating layer formed on the outer surface of the conductivematerial-coating layer and comprising a second polymer binder; aseparation layer surrounding the outer surface of the inner electrode toprevent a short circuit between electrodes; and an outer electrodesurrounding the outer surface of the separation layer and comprising anouter current collector and an outer electrode active material layer.

In the cable-type secondary battery, the open-structured inner currentcollector may be a wound wire form, a wound sheet form or a mesh form.

In the cable-type secondary battery, the inner electrode may be ananode, and the inner electrode active material layer may comprise anactive material selected from the group consisting of metals (Me)including Si, Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce,Cu, Co, Ni and Fe; alloys of the metals; oxides (MeOx) of the metals;and a mixture thereof.

In the outer electrode, the outer electrode active material layer may beformed to surround the outer surface of the separation layer, and theouter current collector may be formed to surround the outer surface ofthe outer electrode active material layer; the outer current collectormay be formed to surround the outer surface of the separation layer, andthe outer electrode active material layer may be formed to surround theouter surface of the outer current collector; the outer currentcollector may be formed to surround the outer surface of the separationlayer, and the outer electrode active material layer may be formed tosurround the outer surface of the outer current collector and come intocontact with the separation layer; or the outer electrode activematerial layer may be formed to surround the outer surface of theseparation layer, and the outer current collector may be formed to beincluded inside the outer electrode active material layer by beingcovered therein and to surround the outer surface of the separationlayer with spacing apart therefrom.

Alternatively, in accordance with still another aspect of the presentinvention, there is provided a cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising: acore for supplying lithium ions, which comprises an electrolyte; aninner electrode comprising an open-structured inner current collectorsurrounding the outer surface of the core for supplying lithium ions,and an inner electrode active material layer surrounding the outersurface of the inner current collector; a separation layer surroundingthe outer surface of the inner electrode to prevent a short circuitbetween electrodes; and an outer electrode surrounding the outer surfaceof the separation layer and comprising an outer current collector, anouter electrode active material layer, a conductive material-coatinglayer comprising a conductive material and a first polymer binder, and aporous coating layer comprising a second polymer binder.

In the cable-type secondary battery, the outer electrode may be ananode, and the outer electrode active material layer may comprise anactive material selected from the group consisting of metals (Me)including Si, Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce,Cu, Co, Ni and Fe; alloys of the metals; oxides (MeOx) of the metals;and a mixture thereof.

In the outer electrode, the porous coating layer comprising a secondpolymer binder may be formed to surround the outer surface of theseparation layer, the conductive material-coating layer comprising aconductive material and a first polymer binder may be formed to surroundthe porous coating layer, the outer electrode active material layer maybe formed to surround the conductive material-coating layer, and theouter current collector may be formed to surround the outer surface ofthe outer electrode active material layer; the outer current collectormay be formed to surround the outer surface of the separation layer, theouter electrode active material layer may be formed to surround theouter surface of the outer current collector, the conductivematerial-coating layer comprising a conductive material and a firstpolymer binder may be formed to surround the outer electrode activematerial layer, and the porous coating layer comprising a second polymerbinder may be formed to surround the conductive material-coating layer;the outer current collector may be formed to surround the outer surfaceof the separation layer, the outer electrode active material layer maybe formed to surround the outer surface of the outer current collectorand come into contact with the separation layer, the conductivematerial-coating layer comprising a conductive material and a firstpolymer binder may be formed to surround the outer electrode activematerial layer, and the porous coating layer comprising a second polymerbinder may be formed to surround the conductive material-coating layer;or the outer electrode active material layer may be formed to surroundthe outer surface of the separation layer, the outer current collectormay be formed to be included inside the outer electrode active materiallayer by being covered therein and to surround the outer surface of theseparation layer with spacing apart therefrom, the conductivematerial-coating layer comprising a conductive material and a firstpolymer binder may be formed to surround the outer electrode activematerial layer, and the porous coating layer comprising a second polymerbinder may be formed to surround the conductive material-coating layer.

Meanwhile, the separation layer may be an electrolyte layer or aseparator.

The electrolyte layer may comprise an electrolyte selected from a gelpolymer electrolyte using PEO, PVdF, PVdF-HFP, PMMA, PAN, or PVAc; and asolid electrolyte using PEO, polypropylene oxide (PPO), polyether imine(PEI), polyethylene sulphide (PES), or polyvinyl acetate (PVAc).

The electrolyte layer may further comprise a lithium salt.

The lithium salt may be selected from LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithiumcarbonate, lithium tetraphenylborate, and a mixture thereof.

The separator may be a porous substrate made of a polyolefin-basedpolymer selected from the group consisting of ethylene homopolymers,propylene homopolymers, ethylene-butene copolymers, ethylene-hexenecopolymers, and ethylene-methacrylate copolymers; a porous substratemade of a polymer selected from the group consisting of polyesters,polyacetals, polyamides, polycarbonates, polyimides, polyether etherketones, polyether sulfones, polyphenylene oxides, polyphenylenesulfides and polyethylene naphthalates; or a porous substrate made of amixture of inorganic particles and a binder polymer.

Also, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising:two or more cores for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector surrounding the outer surface of each core for supplyinglithium ions, an inner electrode active material layer surrounding theouter surface of the inner current collector, a conductivematerial-coating layer formed on the outer surface of the innerelectrode active material layer and comprising a conductive material anda first polymer binder, and a porous coating layer formed on the outersurface of the conductive material-coating layer and comprising a secondpolymer binder; a separation layer surrounding the outer surface of theinner electrodes to prevent a short circuit between electrodes; and anouter electrode surrounding the outer surface of the separation layerand comprising an outer current collector and an outer electrode activematerial layer.

In addition, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising:two or more cores for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector surrounding the outer surface of each core for supplyinglithium ions, an inner electrode active material layer surrounding thesurface of the inner current collector, a conductive material-coatinglayer formed on the outer surface of the inner electrode active materiallayer and comprising a conductive material and a first polymer binder, aporous coating layer formed on the outer surface of the conductivematerial-coating layer and comprising a second polymer binder, and aseparation layer surrounding the outer surface of the porous coatinglayer to prevent a short circuit between electrodes; and an outerelectrode surrounding the outer surface of the inner electrodes andcomprising an outer current collector and an outer electrode activematerial layer.

Further, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising:two or more cores for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector surrounding the outer surface of each core for supplyinglithium ions, and an inner electrode active material layer surroundingthe surface of the inner current collector; a separation layersurrounding the outer surface of the inner electrodes to prevent a shortcircuit between electrodes; and an outer electrode surrounding the outersurface of the separation layer and comprising an outer currentcollector, an outer electrode active material layer, a conductivematerial-coating layer comprising a conductive material and a firstpolymer binder, and a porous coating layer comprising a second polymerbinder.

Furthermore, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising:two or more cores for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector surrounding the outer surface of each core for supplyinglithium ions, an inner electrode active material layer surrounding thesurface of the inner current collector, and a separation layersurrounding the outer surface of the inner electrode active materiallayer to prevent a short circuit between electrodes; and an outerelectrode surrounding the outer surface of the inner electrodes andcomprising an outer current collector, an outer electrode activematerial layer, a conductive material-coating layer comprising aconductive material and a first polymer binder, and a porous coatinglayer comprising a second polymer binder.

Advantageous Effects

In accordance with the present invention, an electrode active materiallayer can be prevented from being released owing to stress generated byexternal force for the shape variation of cable-type secondary batteriesand the like or owing to its rapid volume expansion during charging anddischarging processes, thereby minimizing a capacity decrease in thebatteries and increasing the conductivity of electrodes to provideenhanced cycle life characteristics in the batteries.

Also, the present invention can allow the good introduction of anelectrolyte solution in an electrode active material layer to preventthe increase of electrode resistance, and can prevent the generation ofcracks in a conductive material-coating layer formed on the top surfaceof an electrode active material layer or can prevent the release of theconductive material-coating layer when external forces are applied forbending or twisting.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of thepresent invention and, together with the foregoing disclosure, serve toprovide further understanding of the technical spirit of the presentinvention. However, the present invention is not to be construed asbeing limited to the drawings.

FIG. 1 is a perspective view showing an electrode for a cable-typesecondary battery, comprising a wire current collector, in accordancewith one embodiment of the present invention.

FIG. 2 is a perspective view showing an electrode for a cable-typesecondary battery, comprising a hollow current collector, in accordancewith one embodiment of the present invention.

FIG. 3 is a perspective view showing a cable-type secondary batteryhaving one inner electrode in accordance with one embodiment of thepresent invention.

FIG. 4 is a perspective view showing a cable-type secondary batteryhaving one inner electrode in accordance with another embodiment of thepresent invention.

FIG. 5 is a cross-sectional view showing a cable-type secondary batteryhaving two or more inner electrodes in accordance with one embodiment ofthe present invention.

FIG. 6 is a cross-sectional view showing a cable-type secondary batteryhaving two or more inner electrodes in accordance with anotherembodiment of the present invention.

FIG. 7 is an SEM photograph of a wire electrode having a conductivematerial-coating layer, prepared in the Example of the presentinvention.

FIG. 8 is SEM photographs showing the shape of a porous coating layerobtained in the Example of the present invention.

FIG. 9 is a graph showing the results of charging and dischargingcharacteristics evaluated for batteries prepared in the Example and theComparative Example of the present invention.

EXPLANATION OF REFERENCE NUMERALS

-   -   10, 20: Electrode for cable-type secondary battery    -   11: Wire current collector    -   12. 22: Electrode active material layer    -   13, 23: Conductive material-coating layer    -   14, 24: Porous coating layer    -   21: Hollow current collector    -   100, 200, 300, 400: Cable-type secondary battery    -   110, 210, 310, 410: Core for supplying lithium ions    -   120, 220, 320, 420: Inner current collector    -   130, 230, 330, 430: Inner electrode active material layer    -   140, 240, 340, 440: Separation layer    -   150, 250, 350, 450: Outer electrode active material layer    -   160, 260, 360, 460: Outer current collector    -   170, 270, 370, 470: Protection coating    -   131, 251, 331, 451: Conductive material-coating layer    -   132, 252, 332, 452: Porous coating layer

BEST MODE

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings. Prior to the description, itshould be understood that the terms used in the specification and theappended claims should not be construed as limited to general anddictionary meanings, but interpreted based on the meanings and conceptscorresponding to technical aspects of the present invention on the basisof the principle that the inventor is allowed to define termsappropriately for the best explanation.

Also, the configurations illustrated in the drawings and the embodimentsare just preferable examples for the purpose of illustrations only, notintended to limit the scope of the disclosure, so it should beunderstood that other equivalents and modifications could be madethereto without departing from the spirit and scope of the disclosure.

The electrode for a secondary battery according to the present inventioncomprises a current collector; an electrode active material layer formedon at least one surface or the whole outer surface of the currentcollector; a conductive material-coating layer formed on the top surfaceof the electrode active material layer and comprising a conductivematerial and a first polymer binder; and a porous coating layer formedon the top surface of the conductive material-coating layer andcomprising a second polymer binder.

The current collector used in the electrode of the present invention maybe a planar form, a hollow form, a wire form, a wound wire form, a woundsheet form or a mesh form, but is not limited thereto. Various kinds ofcurrent collectors may be used depending on the forms of secondarybatteries.

In the case that a planar current collector is used, the electrodeactive material layer may be formed on at least one surface of the topand bottom surfaces of the current collector. In the case that a hollowcurrent collector is used, the electrode active material layer may beformed on at least one surface of the inner or outer surfaces of thecurrent collector. In the case that a wire current collector is used,the electrode active material layer may be formed on the whole surfaceof the current collector. In the case that a current collector of awound wire, wound sheet or mesh form is used, the electrode activematerial layer may be formed on at least one surface of the inner orouter surfaces of the current collector or may be formed to surround thewhole surface of the current collector.

FIG. 1 is a perspective view showing an electrode for a cable-typesecondary battery, comprising a wire current collector, in accordancewith one embodiment of the present invention. FIG. 2 is a perspectiveview showing an electrode for a cable-type secondary battery, comprisinga hollow current collector, in accordance with one embodiment of thepresent invention.

Referring to FIG. 1, an electrode 10 for a cable-type secondary batteryextends longitudinally, and comprises a wire current collector 11; anelectrode active material layer 12 formed to surround the whole outersurface of the wire current collector 11; a conductive material-coatinglayer 13 formed to surround the top surface of the electrode activematerial layer 12 and comprising a conductive material and a firstpolymer binder; and a porous coating layer 14 formed to surround the topsurface of the conductive material-coating layer 13 and comprising asecond polymer binder. The electrode 10 for a cable-type secondarybattery may be used as the inner electrode of the cable-type secondarybattery by winding one or more wire in a coil form, or by twisting twoor more wires spirally to obtain one or more wire complex and windingthe wire complex in a coil form.

Referring to FIG. 2, an electrode 20 for a cable-type secondary batteryextends longitudinally, and comprises a hollow current collector 21; anelectrode active material layer 22 formed on the outer surface of thehollow current collector 21; a conductive material-coating layer 23formed to surround the top surface of the electrode active materiallayer 22 and comprising a conductive material and a first polymerbinder; and a porous coating layer 24 formed on the top surface of theconductive material-coating layer 23 and comprising a second polymerbinder. The electrode 20 for a cable-type secondary battery may be usedas the outer electrode of the cable-type secondary battery.

In the electrode for a cable-type secondary battery, the electrodeactive material layer formed on the current collector may be released orcompletely peeled off from the current collector owing to stressgenerated by external force for the shape variation of the battery orowing to its rapid volume expansion during charging and dischargingprocesses. As a result, the electrical conductivity of the electrode isreduced, making it difficult to provide sufficient capacity in thebattery, thereby obtaining a low initial efficiency. Particularly, inthe case of a metal-based anode active material layer formed byelectroplating or anodic oxidation, such a release may be severe due tothe absence of a polymer binder and a conductive material.

In order to prevent such a problem, in the electrode of the presentinvention, a conductive material-coating layer which comprises aconductive material and a first polymer binder is formed on the outersurface of the electrode active material layer, a porous coating layerwhich comprises a second polymer binder is formed on the outer surfaceof the conductive material-coating layer. Thereby, the electrode of thepresent invention can be inhibited from the release of the electrodeactive material layer, thereby preventing a capacity decrease inbatteries, and its conductivity becomes increased to provide enhancedcycle life characteristics in the batteries.

In the present invention, the conductive material-coating layer canserves as a buffer region which can minimize the release of theelectrode active material layer, and can contribute to increase aninitial efficiency and improve cycle life characteristics due to thepresence of a conductive material having good conductivity.

Also, since the release of the electrode active material layer isinhibited even if external forces are applied during battery bending,the flexibility of cable-type batteries can be improved. Further, in theelectrode of the present invention, an electrolyte solution can bebetter introduced in the electrode active material layer through porespresent in the porous coating layer, thereby preventing the increase ofelectrode resistance and eventually enhancing battery performances.

In the conductive material-coating layer, the conductive material andthe first polymer binder may be present in a weight ratio of 1:10 to8:10. When the weight ratio satisfies such numerical range, it canachieve the effects of inhibiting the release of the electrode activematerial layer and providing conductivity in the electrode activematerial layer to increase an initial efficiency and improve lifecharacteristics.

Meanwhile, in the conductive material-coating layer, pores may be formedto allow the introduction of an electrolyte solution. The pores presentin the conductive material-coating layer should have a size smaller thanthat of particles composing the electrode active material layer so as toinhibit the release of the electrode active material layer. Also, it ispreferred that the pores have a size greater than the radius of solvatedlithium ions in the electrolyte solution so as for the electrolytesolution to be well introduced in the electrode. To meet suchconditions, the pores present in the conductive material-coating layermay have a size of 0.01 to 5 μm, and the conductive material-coatinglayer may have a porosity of 5 to 70%.

The conductive material which may be used in the present invention isnot particularly limited if it has conductivity and does not cause achemical change in secondary batteries. For example, carbon black,acetylene black, ketjen black, carbon fiber, carbon nanotube andgraphene which are generally known as a conductive material may be used,and also metal powders, conductive metal oxide and organic conductiveagent may be used. Examples of a commercially available conductivematerial include acetylene black-based products (Chevron ChemicalCompany or Gulf Oil Company), EC-based products (Armak Company), Vulcan,XC-72 (Cabot Company) and Super P (MMM Carbon Company).

Also, the first polymer binder may be selected from the group consistingof polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP),polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidenefluoride-co-trichloroethylene, polybutyl acrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate,polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate,cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof, but is not limited thereto.

Meanwhile, the porous coating layer may be formed to have a porousstructure by phase separation or phase change during its preparation.

The pores formed in the porous coating layer should have a size smallerthan that of particles composing the electrode active material layer soas to inhibit the release of the electrode active material layer. Also,it is preferred that the pores have a size greater than the radius ofsolvated lithium ions in the electrolyte solution so as for theelectrolyte solution to be well introduced in the electrode. To meetsuch conditions, the pores present in the porous coating layer may havea size of 0.01 to 10 μm.

Also, in order to achieve the above-mentioned effects, the porouscoating layer may have a porosity of 5 to 95%.

Meanwhile, the porous coating layer may further comprise inorganicparticles.

In such a porous coating layer, the inorganic particles are bound toeach other by the second polymer binder in the state that the inorganicparticles are filled in contact with each other, from which interstitialvolumes are formed between the inorganic particles. The interstitialvolumes between the inorganic particles become empty spaces to formpores.

In the porous coating layer, the inorganic particles and the secondpolymer binder may be present in a weight ratio of 10:90 to 95:5.

The inorganic particles which may be used in the present invention arenot particularly limited if they are electrochemically stable. That is,the inorganic particles which may be used in the present invention arenot particularly limited unless an oxidation-reduction reaction occursin an operating voltage range (for example, 0 to 5 V based on Li/Li⁺) ofan applied electrochemical device. Particularly, inorganic particleshaving ion-transferring ability can increase an ionic conductivity in anelectrochemical device to achieve the performance improvement of thedevice.

For the foregoing reasons, the inorganic particles used in the presentinvention preferably include inorganic particles having a dielectricconstant of 5 or higher, preferably 10 or higher. Examples of theinorganic particles having a dielectric constant of 5 or higher includeBaTiO₃, Pb(Zr_(x), Ti_(1-x))O₃(PZT, 0<x<1),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),(1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (PMN—PT, 0<x<1), hafnia (HfO₂),SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, SiO₂,AlOOH, Al(OH)₃, TiO₂ and a mixture thereof.

Also, the inorganic particles having the ability to transport lithiumions, i.e., lithium-containing inorganic particles which can transferlithium ions without holding them, may be used. Examples of theinorganic particles having the ability to transport lithium ions includelithium phosphate (Li₃PO₄), lithium titanium phosphate(Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3), lithium aluminum titanium phosphate(Li_(x)Al_(y)Ti_(z)(PO₄)₃, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)_(x)O_(y) typeglass (0<x<4, 0<y<13), lithium lanthanum titanate(Li_(x)La_(y)TiO₃,0<x<2, 0<y<3), lithium germanium thiophosphate(Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride(Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass (Li_(x)Si_(y)S_(z), 0<x<3,0<y<2, 0<z<4), P₂S₅ type glass (Li_(x)P_(y)S_(z), 0<x<3, 0<y<3, 0<z<7)inorganic particles, and a mixture thereof.

The inorganic particles are not limited to their size, but arepreferable to have an average diameter of 10 nm to 5 μm, so as to obtaina suitable porosity of the porous coating layer.

The second polymer binder may be selected from the group consisting ofpolyvinylidene fluoride (PVDF), hexafluoro propylene (HFP),polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidenefluoride-co-trichloroethylene, polybutyl acrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate,polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate,cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof, but is not limited thereto.

Meanwhile, the inner current collector is preferably made of stainlesssteel, aluminum, nickel, titanium, sintered carbon, or copper; stainlesssteel treated with carbon, nickel, titanium or silver on the surfacethereof; an aluminum-cadmium alloy; a non-conductive polymer treatedwith a conductive material on the surface thereof; or a conductivepolymer. The outer current collector is preferably made of stainlesssteel, aluminum, nickel, titanium, sintered carbon, or copper; stainlesssteel treated with carbon, nickel, titanium or silver on the surfacethereof; an aluminum-cadmium alloy; a non-conductive polymer treatedwith a conductive material on the surface thereof; a conductive polymer;a metal paste comprising metal powders of Ni, Al, Au, Ag, Pd/Ag, Cr, Ta,Cu, Ba or ITO; or a carbon paste comprising carbon powders of graphite,carbon black or carbon nanotube.

Such a current collector serves to collect electrons generated byelectrochemical reaction of the active material or to supply electronsrequired for the electrochemical reaction. In general, the currentcollector is made of a metal such as copper or aluminum. Especially,when the current collector is made of a non-conductive polymer treatedwith a conductive material on the surface thereof or a conductivepolymer, the current collector has a relatively higher flexibility thanthe current collector made of a metal such as copper or aluminum. Also,a polymer current collector may be used instead of the metal currentcollector to reduce the weight of the battery.

The conductive material may include polyacetylene, polyaniline,polypyrrole, polythiophene, polysulfurnitride, indium tin oxide (ITO),silver, palladium, nickel, etc. The conductive polymer may includepolyacetylene, polyaniline, polypyrrole, polythiophene,polysulfurnitride, etc. However, the non-conductive polymer used for thecurrent collector is not particularly limited to its kinds.

Meanwhile, the electrode for a secondary battery may be used as ananode. In this case, the electrode active material layer may comprise anactive material selected from the group consisting of metals (Me)including Si, Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce,Cu, Co, Ni and Fe; alloys of the metals; oxides (MeOx) of the metals;and a mixture thereof.

In the present invention, the electrode active material layer allowsions to move through the current collector, and the movement of ions iscaused by the interaction of ions such as intercalation/deintercalationof ions into and from the electrolyte layer.

Also, the present invention provides a secondary battery comprising acathode, an anode, a separator interposed between the cathode and theanode, and a non-aqueous electrolyte solution, wherein the anode is theabove-mentioned electrode for a secondary battery according to thepresent invention.

The secondary battery of the present invention may be in the generalform of stacking, winding or stacking/folding, and also it may be in theparticular form of cable type.

Specifically, a cable-type secondary battery according to one aspect ofthe present invention, which has a horizontal cross section and extendslongitudinally, comprises a core for supplying lithium ions, whichcomprises an electrolyte; an inner electrode comprising anopen-structured inner current collector surrounding the outer surface ofthe core for supplying lithium ions, an inner electrode active materiallayer surrounding the outer surface of the inner current collector, aconductive material-coating layer formed on the outer surface of theinner electrode active material layer and comprising a conductivematerial and a first polymer binder, and a porous coating layer formedon the outer surface of the conductive material-coating layer andcomprising a second polymer binder; a separation layer surrounding theouter surface of the inner electrode to prevent a short circuit betweenelectrodes; and an outer electrode surrounding the outer surface of theseparation layer and comprising an outer current collector and an outerelectrode active material layer.

As used herein, the term ‘open-structured’ means that a structure has anopen boundary surface through which a substance may be transferredfreely from the inside of the structure to the outside thereof. Theopen-structured inner current collector may be in the form of a woundwire, a wound sheet or a mesh, but is not limited thereto.

Also, the term ‘a horizontal cross section’ may refer to a circular orpolygonal shape. The circular shape includes circles having a perfectlysymmetrical geometric structure and ovals having an asymmetricalstructure. The polygonal shape is not limited to any particular form,but examples thereof may include triangular, tetragonal, pentagonal andhexagonal forms.

As mentioned above, the porous coating layer may further compriseinorganic particles.

In the cable-type secondary battery, the inner electrode may be ananode, and the inner electrode active material layer may comprise anactive material selected from the group consisting of metals (Me)including Si, Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce,Cu, Co, Ni and Fe; alloys of the metals; oxides (MeOx) of the metals;and a mixture thereof.

Also, the outer electrode may be a cathode, and the outer activematerial layer may comprise a cathode active material selected from thegroup consisting of LiCoO₂, LiNiO₂, LiMn₂O₄, LiCoPO₄, LiFePO₄,LiNiMnCoO₂, LiNi_(1-x-y-z)Co_(x)M1_(y)M2_(z)O₂ (wherein M1 and M2 areeach independently selected from the group consisting of Al, Ni, Co, Fe,Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are each independentlyan atomic fraction of oxide-forming elements, in which 0≦x<0.5, 0≦y<0.5,0≦z<0.5, and x+y+z≦1), and a mixture thereof.

The cable-type secondary battery of the present invention has ahorizontal cross section with a linear structure which extends in thelongitudinal direction, and thus has flexibility, so it can freelychange in shape.

FIG. 3 is a perspective view showing a cable-type secondary batteryhaving one inner electrode in accordance with one embodiment of thepresent invention.

Referring to FIG. 3, a cable-type secondary battery 100 comprises a core110 for supplying lithium ions, which comprises an electrolyte; an innerelectrode comprising an open-structured inner current collector 120surrounding the outer surface of the core 110 for supplying lithiumions, an inner electrode active material layer 130 surrounding the outersurface of the inner current collector 120, a conductivematerial-coating layer 131 formed on the outer surface of the innerelectrode active material layer 130 and comprising a conductive materialand a first polymer binder, and a porous coating layer 132 formed on theouter surface of the conductive material-coating layer 131 andcomprising a second polymer binder; a separation layer 140 surroundingthe outer surface of the inner electrode to prevent a short circuitbetween electrodes; and an outer electrode comprising an outer electrodeactive material layer 150 surrounding the outer surface of theseparation layer 140 and an outer current collector 160 surrounding theouter surface of the outer electrode active material layer 150.

Besides such structure, the outer electrode may be configured withvarious structures depending on the disposition of the outer currentcollector and the outer electrode active material. For example, theouter electrode may be configured with a structure having the outercurrent collector formed to surround the outer surface of the separationlayer, and the outer electrode active material layer formed to surroundthe outer surface of the outer current collector; a structure having theouter current collector formed to surround the outer surface of theseparation layer, and the outer electrode active material layer formedto surround the outer surface of the outer current collector and comeinto contact with the separation layer; or a structure having the outerelectrode active material layer formed to surround the outer surface ofthe separation layer, and the outer current collector formed to beincluded inside the outer electrode active material layer by beingcovered therein and to surround the outer surface of the separationlayer with spacing apart therefrom.

Meanwhile, a cable-type secondary battery according to another aspect ofthe present invention, which has a horizontal cross section and extendslongitudinally, comprises a core for supplying lithium ions, whichcomprises an electrolyte; an inner electrode comprising anopen-structured inner current collector surrounding the outer surface ofthe core for supplying lithium ions, and an inner electrode activematerial layer surrounding the outer surface of the inner currentcollector; a separation layer surrounding the outer surface of the innerelectrode to prevent a short circuit between electrodes; and an outerelectrode surrounding the outer surface of the separation layer andcomprising an outer current collector, an outer electrode activematerial layer, a conductive material-coating layer comprising aconductive material and a first polymer binder, and a porous coatinglayer comprising a second polymer binder.

As mentioned above, the porous coating layer may further compriseinorganic particles.

In such cable-type secondary battery, the outer electrode may be ananode, and the outer electrode active material layer may comprise anactive material as mentioned above.

FIG. 4 is a perspective view showing a cable-type secondary batteryaccording to one embodiment of the present invention, in which aconductive material-coating layer and a porous coating layer are formedon an outer electrode.

Referring to FIG. 4, a cable-type secondary battery 200 comprises a core210 for supplying lithium ions, which comprises an electrolyte; an innerelectrode comprising an open-structured inner current collector 220surrounding the outer surface of the core 210 for supplying lithiumions, and an inner electrode active material layer 230 surrounding theouter surface of the inner current collector 220; a separation layer 240surrounding the outer surface of the inner electrode to prevent a shortcircuit between electrodes; and an outer electrode, comprising a porouscoating layer 252 surrounding the outer surface of the separation layer240 and comprising a second polymer binder, a conductivematerial-coating layer 251 surrounding the porous coating layer 252 andcomprising a conductive material and a first polymer binder, an outerelectrode active material layer 250 surrounding the conductivematerial-coating layer 251, and an outer current collector 260surrounding the outer surface of the outer electrode active materiallayer 250.

Besides such structure, the outer electrode may be configured withvarious structures depending on the disposition of the conductivematerial-coating layer and the porous coating layer. For example, theouter electrode may be configured with a structure having the outercurrent collector formed to surround the outer surface of the separationlayer, the outer electrode active material layer formed to surround theouter surface of the outer current collector, the conductivematerial-coating layer formed to surround the outer electrode activematerial layer and comprising a conductive material and a first polymerbinder, and the porous coating layer formed to surround the conductivematerial-coating layer and comprising a second polymer binder; astructure having the outer current collector formed to surround theouter surface of the separation layer, the outer electrode activematerial layer formed to surround the outer surface of the outer currentcollector and come into contact with the separation layer, theconductive material-coating layer formed to surround the outer electrodeactive material layer and comprising a conductive material and a firstpolymer binder, and the porous coating layer formed to surround theconductive material-coating layer and comprising a second polymerbinder; or a structure having the outer electrode active material layerformed to surround the outer surface of the separation layer, the outercurrent collector formed to be included inside the outer electrodeactive material layer by being covered therein and to surround the outersurface of the separation layer with spacing apart therefrom, theconductive material-coating layer formed to surround the outer electrodeactive material layer and comprising a conductive material and a firstpolymer binder, and the porous coating layer formed to surround theconductive material-coating layer and comprising a second polymerbinder.

Meanwhile, in the present invention, the separation layer may be anelectrolyte layer or a separator.

The electrolyte layer serving as an ion channel may be made of agel-type polymer electrolyte using PEO, PVdF, PVdF-HFP, PMMA, PAN orPVAC, or a solid electrolyte using PEO, polypropylene oxide (PPO),polyethylene imine (PEI), polyethylene sulfide (PES) or polyvinylacetate (PVAc). The matrix of the solid electrolyte is preferably formedusing a polymer or a ceramic glass as the backbone. In the case oftypical polymer electrolytes, the ions move very slowly in terms ofreaction rate, even when the ionic conductivity is satisfied. Thus, thegel-type polymer electrolyte which facilitates the movement of ions ispreferably used compared to the solid electrolyte. The gel-type polymerelectrolyte has poor mechanical properties and thus may comprise aporous support or a cross-linked polymer to improve poor mechanicalproperties. The electrolyte layer of the present invention can serve asa separator, and thus an additional separator may be omitted.

In the present invention, the electrolyte layer may further comprise alithium salt. The lithium salt can improve an ionic conductivity andresponse time. Non-limiting examples of the lithium salt may includeLiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂,LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi, lithiumchloroborate, lower aliphatic lithium carbonate, and lithiumtetraphenylborate.

Examples of the separator may include, but is not limited to, a poroussubstrate made of a polyolefin-based polymer selected from the groupconsisting of ethylene homopolymers, propylene homopolymers,ethylene-butene copolymers, ethylene-hexene copolymers, andethylene-methacrylate copolymers; a porous substrate made of a polymerselected from the group consisting of polyesters, polyacetals,polyamides, polycarbonates, polyimides, polyether ether ketones,polyether sulfones, polyphenylene oxides, polyphenylene sulfides andpolyethylene naphthalates; or a porous substrate made of a mixture ofinorganic particles and a binder polymer. Among these, in order for thelithium ions of the core for supplying lithium ions to be transferred tothe outer electrode, it is preferred to use a non-woven fabric separatorcorresponding to the porous substrate made of a polymer selected fromthe group consisting of polyesters, polyacetals, polyamides,polycarbonates, polyimides, polyether ether ketones, polyether sulfones,polyphenylene oxides, polyphenylene sulfides and polyethylenenaphthalates.

Also, the cable-type secondary battery of the present invention has aprotection coating. The protection coating is an insulator and is formedto surround the outer current collector, thereby protecting theelectrodes against moisture in the air and external impacts. Theprotection coating may be made of conventional polymer resins, forexample, PVC, HDPE or epoxy resins.

Meanwhile, a cable-type secondary battery according to still anotherembodiment of the present invention comprises two or more innerelectrodes.

In the battery having two or more inner electrodes, when the innerelectrodes are used as an anode, the battery comprises two or more coresfor supplying lithium ions, which comprise an electrolyte; two or moreinner electrodes arranged in parallel to each other, each innerelectrode comprising an open-structured inner current collectorsurrounding the outer surface of each core for supplying lithium ions,an inner electrode active material layer surrounding the outer surfaceof the inner current collector, a conductive material-coating layerformed on the outer surface of the inner electrode active material layerand comprising a conductive material and a first polymer binder, and aporous coating layer formed on the outer surface of the conductivematerial-coating layer and comprising a second polymer binder; aseparation layer surrounding the outer surface of the inner electrodesto prevent a short circuit between electrodes; and an outer electrodesurrounding the outer surface of the separation layer and comprising anouter current collector and an outer electrode active material layer.Also, the battery may be configured to comprise two or more cores forsupplying lithium ions, which comprise an electrolyte; two or more innerelectrodes arranged in parallel to each other, each inner electrodecomprising an open-structured inner current collector surrounding theouter surface of each core for supplying lithium ions, an innerelectrode active material layer surrounding the surface of the innercurrent collector, a conductive material-coating layer formed on theouter surface of the inner electrode active material layer andcomprising a conductive material and a first polymer binder, a porouscoating layer formed on the outer surface of the conductivematerial-coating layer and comprising a second polymer binder, and aseparation layer surrounding the outer surface of the porous coatinglayer to prevent a short circuit between electrodes; and an outerelectrode surrounding the outer surface of the inner electrodes andcomprising an outer current collector and an outer electrode activematerial layer.

In the battery, the porous coating layer may further comprise inorganicparticles as mentioned above.

Hereinafter, FIG. 5 will be specifically described.

Referring to FIG. 5, a cable-type secondary battery 300, which hasmultiple inner electrodes according to the present invention, comprisestwo or more cores 310 for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector 320 surrounding the outer surface of each core 310 forsupplying lithium ions, an inner electrode active material layer 330surrounding the outer surface of the inner current collector 320, aconductive material-coating layer 331 formed on the outer surface of theinner electrode active material layer 330 and comprising a conductivematerial and a first polymer binder, and a porous coating layer 332formed on the outer surface of the conductive material-coating layer 331and comprising a second polymer binder; a separation layer 340surrounding the outer surface of the inner electrodes to prevent a shortcircuit between electrodes; and an outer electrode comprising an outerelectrode active material layer 350 surrounding the outer surface of theseparation layer 340 and an outer current collector 360 surrounding theouter surface of the outer electrode active material layer 350.

Meanwhile, in the battery having two or more inner electrodes, when anouter electrode is used as an anode, the battery comprises two or morecores for supplying lithium ions, which comprise an electrolyte; two ormore inner electrodes arranged in parallel to each other, each innerelectrode comprising an open-structured inner current collectorsurrounding the outer surface of each core for supplying lithium ions,and an inner electrode active material layer surrounding the surface ofthe inner current collector; a separation layer surrounding the outersurface of the inner electrodes to prevent a short circuit betweenelectrodes; and an outer electrode surrounding the outer surface of theseparation layer and comprising an outer current collector, an outerelectrode active material layer, a conductive material-coating layercomprising a conductive material and a first polymer binder, and aporous coating layer comprising a second polymer binder. Also, thebattery may be configured to comprise two or more cores for supplyinglithium ions, which comprise an electrolyte; two or more innerelectrodes arranged in parallel to each other, each inner electrodecomprising an open-structured inner current collector surrounding theouter surface of each core for supplying lithium ions, an innerelectrode active material layer surrounding the surface of the innercurrent collector, and a separation layer surrounding the outer surfaceof the inner electrode active material layer to prevent a short circuitbetween electrodes; and an outer electrode surrounding the outer surfaceof the inner electrodes and comprising an outer current collector, anouter electrode active material layer, a conductive material-coatinglayer comprising a conductive material and a first polymer binder, and aporous coating layer comprising a second polymer binder.

In the battery, the porous coating layer may further comprise inorganicparticles as mentioned above.

Hereinafter, FIG. 6 will be specifically described.

Referring to FIG. 6, a cable-type secondary battery 400 comprises two ormore cores 410 for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode comprising an open-structured inner currentcollector 420 surrounding the outer surface of each core 410 forsupplying lithium ions, and an inner electrode active material layer 430surrounding the surface of the inner current collector 420; a separationlayer 440 surrounding the outer surface of the inner electrodes toprevent a short circuit between electrodes; and an outer electrode,comprising a porous coating layer 452 surrounding the outer surface ofthe separation layer 440 and comprising a second polymer binder, theconductive material-coating layer 451 surrounding the porous coatinglayer 452 and comprising a conductive material and a first polymerbinder, the outer electrode active material layer 450 surrounding theconductive material-coating layer 451, and the outer current collector460 surrounding the outer surface of the outer electrode active materiallayer 450.

Besides such structure, the outer electrode may be configured withvarious structures as mentioned above.

Such cable-type secondary batteries 300 and 400 have the inner electrodeconsisting of multiple electrodes, thereby allowing controlling thebalance between a cathode and anode and preventing a short circuit.

Hereinafter, the present invention will be described in detail throughspecific examples. However, the description proposed herein is just apreferable example for the purpose of illustrations only, not intendedto limit the scope of the invention, so it should be understood that theexamples are provided for a more definite explanation to an ordinaryperson skilled in the art.

Example (1) Preparation of Electrode

A copper wire current collector (diameter 125 μm) was coated with anelectrode active material comprising nickel and tin in a thickness of2.5 μm by an electroplating process, to form an electrode activematerial layer.

Then, carbon fiber as a conductive material and polyvinylidene fluorideas a first polymer binder were mixed in a weight ratio of 60:40, and themixture was added to N-methylpyrrolydone used as a solvent, to obtain aslurry. The slurry was coated on the whole outer surface of theelectrode active material layer to form a conductive material-coatinglayer.

FIG. 7 is an SEM photograph of a wire electrode having a conductivematerial-coating layer.

Subsequently, silicon oxide (SiO₂) as inorganic particles andpolyvinylidene fluoride-co-hexafluoro propylene (PVdF-HFP, 5%) as asecond binder were mixed in a weight ratio of 10:90, and the mixture wasadded to an acetone solvent to obtain a solution containing the mixturein an amount of 6 wt %.

To the obtained solution, water is added as a non-solvent such that theamount of the mixture became 5 wt % based on the total weight of thesolution.

The solution thus finally obtained was coated on the whole outer surfaceof the conductive material-coating layer, and the acetone solvent wasevaporated at room temperature, followed by drying in a vacuum oven setto 100° C. for 10 hours, to form a porous coating layer.

FIG. 8 is SEM photographs showing the shape of a porous coating layerobtained by such procedures.

(2) Preparation of Coin-Type Half-Cell

The wire electrode prepared in step (1) was wound on a horizontal planeto produce a plate form, and was used as an anode. As a cathode, ametallic lithium foil was used. A polyethylene separator was interposedbetween the cathode and the anode to obtain an electrode assembly.

The electrode assembly was put in a battery case, to which 1M LiPF₆ ofnon-aqueous electrolyte solution was introduced, the electrolytesolution being obtained by mixing ethylene carbonate (EC) and diethylcarbonate (DEC) in a volume ratio of 1:2 and adding LiPF₆ to theresulting non-aqueous solvent until the concentration of LiPF₆ became1M. Thereby, a coin-type half-cell was prepared.

Comparative Example (1) Preparation of Electrode

A copper wire current collector (diameter 125 μm) was coated with anelectrode active material comprising nickel and tin in a thickness of2.5 μm by an electroplating process, to form an electrode activematerial layer.

(2) Preparation of Coin-Type Half-Cell

The wire electrode prepared in step (1) was wound on a horizontal planeto produce a plate form, and was used as an anode. Other procedures werecarried out in the same manners as in step (2) of Example 1, to preparea coin-type half-cell.

Evaluation of Charge/Discharge Characteristics

The half-cells prepared in the Example and the Comparative Example wereeach evaluated for their charge/discharge characteristics.

The batteries were charged with a current density of 0.1 C up to 5 mV atconstant current and then continuously charged with 5 mV at constantvoltage, and the charging process was completed when the current densityreached 0.005 C. Then, batteries were discharged with a current densityof 0.5 C up to 1.5 V at constant current. The charging/discharging wasrepeated 30 times under the same conditions.

FIG. 9 is a graph showing cycle life characteristics of the batteriesprepared in the Example and the Comparative Example during 30 cycles ofcharging/discharging processes.

As shown in FIG. 9, the battery of the Comparative Example exhibited acapacity decrease by about 20% after 30 cycles, whereas the battery ofthe Example maintained 70% or more of capacity. From this, it wasconfirmed that the battery of the Example had superior cycle lifecharacteristics than the battery of the Comparative Example.

Meanwhile, the batteries were measured for their initial efficiencyafter the first cycle. The results thereof are shown in Table 1, fromwhich the battery of the Example was confirmed to have good initialefficiency.

TABLE 1 Discharge Charge Capacity Capacity Efficiency of First Cycle(mAh/g) (mAh/g) (%) Example 888 790 88.9 Com. Example 868 640 73.7

Meanwhile, the embodiments proposed in the disclosure and the drawingsare just specific examples for the better understanding of the presentinvention, and are not intended to limit the scope of the invention.Therefore, it is obvious to an ordinary person skilled in the art thatother equivalents and modifications could be made thereto withoutdeparting from the spirit and scope of the disclosure.

What is claimed is:
 1. An electrode for a secondary battery, comprisinga current collector; an electrode active material layer formed on atleast one surface or the whole outer surface of the current collector; aconductive material-coating layer formed on the top surface of theelectrode active material layer and comprising a conductive material anda first polymer binder; and a porous coating layer formed on the topsurface of the conductive material-coating layer and comprising a secondpolymer binder.
 2. The electrode according to claim 1, wherein thecurrent collector is a planar form, a hollow form, a wire form, a woundwire form, a wound sheet form or a mesh form.
 3. The electrode accordingto claim 1, wherein the conductive material and the first polymer binderin the conductive material-coating layer are present in a weight ratioof 1:10 to 8:10.
 4. The electrode according to claim 1, wherein theconductive material-coating layer has pores having a size of 0.01 to 5μm, and a porosity of 5 to 70%
 5. The electrode according to claim 1,wherein the conductive material comprises any one selected from thegroup consisting of carbon black, acetylene black, ketjen black, carbonfiber, carbon nanotube, graphene and a mixture thereof
 6. The electrodeaccording to claim 1, wherein the first polymer binder is selected fromthe group consisting of polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), polyvinylidene fluoride-co-hexafluoro propylene,polyvinylidene fluoride-co-trichloroethylene, polybutyl acrylate,polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone,polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide,polyarylate, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.
 7. The electrode accordingto claim 1, wherein the porous coating layer has pores having a size of0.01 to 10 μm, and a porosity of 5 to 95%.
 8. The electrode according toclaim 1, wherein the porous coating layer further comprises inorganicparticles
 9. The electrode according to claim 8, wherein the inorganicparticles and the second polymer binder in the porous coating layer arepresent in a weight ratio of 10:90 to 95:5.
 10. The electrode accordingto claim 8, wherein the inorganic particles are inorganic particleshaving a dielectric constant of 5 or higher, inorganic particles havingthe ability to transport lithium ions, or a mixture thereof.
 11. Theelectrode according to claim 10, wherein the inorganic particles havinga dielectric constant of 5 or higher are selected from the groupconsisting of BaTiO₃, Pb(Zr_(x), Ti_(1-x))O₃(PZT, 0<x<1),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),(1−x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (PMN—PT, 0<x<1), hafnia (HfO₂),SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, SiO₂,AlOOH, Al(OH)₃, TiO₂ and a mixture thereof.
 12. The electrode accordingto claim 10, wherein the inorganic particles having the ability totransport lithium ions are selected from the group consisting of lithiumphosphate (Li₃PO₄), lithium titanium phosphate (Li_(x)Ti_(y)(PO₄)₃,0<x<2, 0<y<3), lithium aluminum titanium phosphate(Li_(x)Al_(y)Ti_(z)(PO₄)₃, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)_(x)O_(y) typeglass (0<x<4, 0<y<13), lithium lanthanum titanate(Li_(x)La_(y)TiO₃,0<x<2, 0<y<3), lithium germanium thiophosphate(Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride(Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass (Li_(x)Si_(y)S_(z), 0<x<3,0<y<2, 0<z<4), P₂S₅ type glass (Li_(x)P_(y)S_(z), 0<x<3, 0<y<3, 0<z<7)inorganic particles, and a mixture thereof.
 13. The electrode accordingto claim 8, wherein the inorganic particles have an average diameter of10 nm to 5 μm.
 14. The electrode according to claim 1, wherein thesecond polymer binder is selected from the group consisting ofpolyvinylidene fluoride (PVDF), hexafluoro propylene (HFP),polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidenefluoride-co-trichloroethylene, polybutyl acrylate, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate,polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate,cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.
 15. The electrode accordingto claim 1, which is used as an anode.
 16. The electrode according toclaim 15, wherein the electrode active material layer comprises anactive material selected from the group consisting of metals (Me)including Si, Sn, Li, Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce,Cu, Co, Ni and Fe; alloys of the metals; oxides (MeOx) of the metals;and a mixture thereof.
 17. A secondary battery comprising a cathode, ananode, a separator interposed between the cathode and the anode, and anon-aqueous electrolyte solution, wherein the anode is the electrodeaccording to claim
 1. 18. A cable-type secondary battery having ahorizontal cross section and extending longitudinally, and comprising: acore for supplying lithium ions, which comprises an electrolyte; aninner electrode comprising an open-structured inner current collectorsurrounding the outer surface of the core for supplying lithium ions, aninner electrode active material layer surrounding the outer surface ofthe inner current collector, a conductive material-coating layer formedon the outer surface of the inner electrode active material layer andcomprising a conductive material and a first polymer binder, and aporous coating layer formed on the outer surface of the conductivematerial-coating layer and comprising a second polymer binder; aseparation layer surrounding the outer surface of the inner electrode toprevent a short circuit between electrodes; and an outer electrodesurrounding the outer surface of the separation layer and comprising anouter current collector and an outer electrode active material layer.19. The cable-type secondary battery according to claim 18, wherein theopen-structured inner current collector is a wound wire form, a woundsheet form or a mesh form.
 20. The cable-type secondary batteryaccording to claim 18, wherein the inner electrode is an anode, and theinner electrode active material layer comprises an active materialselected from the group consisting of metals (Me) including Si, Sn, Li,Al, Ag, Bi, In, Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce, Cu, Co, Ni and Fe;alloys of the metals; oxides (MeOx) of the metals; and a mixturethereof.
 21. The cable-type secondary battery according to claim 18,wherein in the outer electrode, the outer electrode active materiallayer is formed to surround the outer surface of the separation layer,and the outer current collector is formed to surround the outer surfaceof the outer electrode active material layer; the outer currentcollector is formed to surround the outer surface of the separationlayer, and the outer electrode active material layer is formed tosurround the outer surface of the outer current collector; the outercurrent collector is formed to surround the outer surface of theseparation layer, and the outer electrode active material layer isformed to surround the outer surface of the outer current collector andcome into contact with the separation layer; or the outer electrodeactive material layer is formed to surround the outer surface of theseparation layer, and the outer current collector is formed to beincluded inside the outer electrode active material layer by beingcovered therein and to surround the outer surface of the separationlayer with spacing apart therefrom.
 22. A cable-type secondary batteryhaving a horizontal cross section and extending longitudinally, andcomprising: a core for supplying lithium ions, which comprises anelectrolyte; an inner electrode comprising an open-structured innercurrent collector surrounding the outer surface of the core forsupplying lithium ions, and an inner electrode active material layersurrounding the outer surface of the inner current collector; aseparation layer surrounding the outer surface of the inner electrode toprevent a short circuit between electrodes; and an outer electrodesurrounding the outer surface of the separation layer and comprising anouter current collector, an outer electrode active material layer, aconductive material-coating layer comprising a conductive material and afirst polymer binder, and a porous coating layer comprising a secondpolymer binder.
 23. The cable-type secondary battery according to claim22, wherein the outer electrode is an anode, and the outer electrodeactive material layer comprises an active material selected from thegroup consisting of metals (Me) including Si, Sn, Li, Al, Ag, Bi, In,Ge, Pb, Pt, Ti, Zn, Mg, Cd, Ce, Cu, Co, Ni and Fe; alloys of the metals;oxides (MeOx) of the metals; and a mixture thereof.
 24. The cable-typesecondary battery according to claim 22, wherein in the outer electrode,the porous coating layer comprising a second polymer binder is formed tosurround the outer surface of the separation layer, the conductivematerial-coating layer comprising a conductive material and a firstpolymer binder is formed to surround the porous coating layer, the outerelectrode active material layer is formed to surround the conductivematerial-coating layer, and the outer current collector is formed tosurround the outer surface of the outer electrode active material layer;the outer current collector is formed to surround the outer surface ofthe separation layer, the outer electrode active material layer isformed to surround the outer surface of the outer current collector, theconductive material-coating layer comprising a conductive material and afirst polymer binder is formed to surround the outer electrode activematerial layer, and the porous coating layer comprising a second polymerbinder is formed to surround the conductive material-coating layer; theouter current collector is formed to surround the outer surface of theseparation layer, the outer electrode active material layer is formed tosurround the outer surface of the outer current collector and come intocontact with the separation layer, the conductive material-coating layercomprising a conductive material and a first polymer binder is formed tosurround the outer electrode active material layer, and the porouscoating layer comprising a second polymer binder is formed to surroundthe conductive material-coating layer; or the outer electrode activematerial layer is formed to surround the outer surface of the separationlayer, the outer current collector is formed to be included inside theouter electrode active material layer by being covered therein and tosurround the outer surface of the separation layer with spacing aparttherefrom, the conductive material-coating layer comprising a conductivematerial and a first polymer binder is formed to surround the outerelectrode active material layer, and the porous coating layer comprisinga second polymer binder is formed to surround the conductivematerial-coating layer.
 25. The cable-type secondary battery accordingto claim 18, wherein the separation layer is an electrolyte layer or aseparator.
 26. The cable-type secondary battery according to claim 25,wherein the electrolyte layer comprises an electrolyte selected from agel polymer electrolyte using PEO, PVdF, PVdF-HFP, PMMA, PAN, or PVAc;and a solid electrolyte using PEO, polypropylene oxide (PPO), polyetherimine (PEI), polyethylene sulphide (PES), or polyvinyl acetate (PVAc).27. The cable-type secondary battery according to claim 26, wherein theelectrolyte layer further comprises a lithium salt.
 28. The cable-typesecondary battery according to claim 27, wherein the lithium salt isselected from LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆,LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li,(CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithium carbonate,lithium tetraphenylborate, and a mixture thereof.
 29. The cable-typesecondary battery according to claim 25, wherein the separator is aporous substrate made of a polyolefin-based polymer selected from thegroup consisting of ethylene homopolymers, propylene homopolymers,ethylene-butene copolymers, ethylene-hexene copolymers, andethylene-methacrylate copolymers; a porous substrate made of a polymerselected from the group consisting of polyesters, polyacetals,polyamides, polycarbonates, polyimides, polyether ether ketones,polyether sulfones, polyphenylene oxides, polyphenylene sulfides andpolyethylene naphthalates; or a porous substrate made of a mixture ofinorganic particles and a binder polymer.
 30. A cable-type secondarybattery having a horizontal cross section and extending longitudinally,and comprising: two or more cores for supplying lithium ions, whichcomprise an electrolyte; two or more inner electrodes arranged inparallel to each other, each inner electrode comprising anopen-structured inner current collector surrounding the outer surface ofeach core for supplying lithium ions, an inner electrode active materiallayer surrounding the outer surface of the inner current collector, aconductive material-coating layer formed on the outer surface of theinner electrode active material layer and comprising a conductivematerial and a first polymer binder, and a porous coating layer formedon the outer surface of the conductive material-coating layer andcomprising a second polymer binder; a separation layer surrounding theouter surface of the inner electrodes to prevent a short circuit betweenelectrodes; and an outer electrode surrounding the outer surface of theseparation layer and comprising an outer current collector and an outerelectrode active material layer.
 31. A cable-type secondary batteryhaving a horizontal cross section and extending longitudinally, andcomprising: two or more cores for supplying lithium ions, which comprisean electrolyte; two or more inner electrodes arranged in parallel toeach other, each inner electrode comprising an open-structured innercurrent collector surrounding the outer surface of each core forsupplying lithium ions, an inner electrode active material layersurrounding the surface of the inner current collector, a conductivematerial-coating layer formed on the outer surface of the innerelectrode active material layer and comprising a conductive material anda first polymer binder, a porous coating layer formed on the outersurface of the conductive material-coating layer and comprising a secondpolymer binder, and a separation layer surrounding the outer surface ofthe porous coating layer to prevent a short circuit between electrodes;and an outer electrode surrounding the outer surface of the innerelectrodes and comprising an outer current collector and an outerelectrode active material layer.
 32. A cable-type secondary batteryhaving a horizontal cross section and extending longitudinally, andcomprising: two or more cores for supplying lithium ions, which comprisean electrolyte; two or more inner electrodes arranged in parallel toeach other, each inner electrode comprising an open-structured innercurrent collector surrounding the outer surface of each core forsupplying lithium ions, and an inner electrode active material layersurrounding the surface of the inner current collector; a separationlayer surrounding the outer surface of the inner electrodes to prevent ashort circuit between electrodes; and an outer electrode surrounding theouter surface of the separation layer and comprising an outer currentcollector, an outer electrode active material layer, a conductivematerial-coating layer comprising a conductive material and a firstpolymer binder, and a porous coating layer comprising a second polymerbinder.
 33. A cable-type secondary battery having a horizontal crosssection and extending longitudinally, and comprising: two or more coresfor supplying lithium ions, which comprise an electrolyte; two or moreinner electrodes arranged in parallel to each other, each innerelectrode comprising an open-structured inner current collectorsurrounding the outer surface of each core for supplying lithium ions,an inner electrode active material layer surrounding the surface of theinner current collector, and a separation layer surrounding the outersurface of the inner electrode active material layer to prevent a shortcircuit between electrodes; and an outer electrode surrounding the outersurface of the inner electrodes and comprising an outer currentcollector, an outer electrode active material layer, a conductivematerial-coating layer comprising a conductive material and a firstpolymer binder, and a porous coating layer comprising a second polymerbinder.